X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fevaluate.cpp;h=ab71fa67df0cc40161ad0fca2259eb3e82b76058;hb=ad926d34c0105d523bfa5cb92cbcf9f337d54c08;hp=28689f1d4167a33f55c7adf343abbdefda5099a1;hpb=88f17a814d80cdb32ccf9efb7b56bb36d7bf052b;p=stockfish

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 28689f1d..ab71fa67 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1,6 +1,6 @@
 /*
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
-  Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
+  Copyright (C) 2004-2022 The Stockfish developers (see AUTHORS file)
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -1082,22 +1082,28 @@ make_v:
 Value Eval::evaluate(const Position& pos) {
 
   Value v;
+  bool useClassical = false;
 
   // Deciding between classical and NNUE eval (~10 Elo): for high PSQ imbalance we use classical,
   // but we switch to NNUE during long shuffling or with high material on the board.
-
   if (  !useNNUE
       || abs(eg_value(pos.psq_score())) * 5 > (850 + pos.non_pawn_material() / 64) * (5 + pos.rule50_count()))
-      v = Evaluation<NO_TRACE>(pos).value();          // classical
-  else
   {
-       int scale = 1136
-                   + 20 * pos.non_pawn_material() / 1024;
+      v = Evaluation<NO_TRACE>(pos).value();          // classical
+      useClassical = abs(v) >= 300;
+  }
 
+  // If result of a classical evaluation is much lower than threshold fall back to NNUE
+  if (useNNUE && !useClassical)
+  {
        Value nnue     = NNUE::evaluate(pos, true);     // NNUE
+       int scale      = 1136 + 20 * pos.non_pawn_material() / 1024;
        Color stm      = pos.side_to_move();
        Value optimism = pos.this_thread()->optimism[stm];
+       Value psq      = (stm == WHITE ? 1 : -1) * eg_value(pos.psq_score());
+       int complexity = abs(nnue - psq) / 256;
 
+       optimism *= (1 + complexity);
        v = (nnue + optimism) * scale / 1024 - optimism;
 
        if (pos.is_chess960())